Hydronic boilers are used in generating heat for residential and industrial purposes. The hydronic boiler operates by heating water to a preset temperature and circulating the water throughout the building, typically by way of radiators, baseboard heaters, or through the floors. Typically, the water is heated by a natural gas burner. The water is in an enclosed system and circulated throughout the structure by a pump.
Hydronic boilers typically include a pressure vessel with internal heat exchange tubes in contact with flowing water. In one type of water heating apparatus, known as a fire tube boiler, hot combustion gases flow internally through the heat exchange tubes and the water to be heated flows around the tubes, picking up the heat. In another type of conventional water heating apparatus, water rapidly flows within the heat exchange tubes and the heat source is exposed to the outside of the tubes.
The water volume of a hydronic boiler pressure vessel is a function of the building's thermal demand and the output capacity of the heat exchange system. The operating water pressure in a hydronic boiler can be as high as 80 psi or even 160 psi. Therefore, in large-scale or industrial hydronic boilers, the pressure vessel may be quite large, over four feet in diameter.